Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2015

Activity Under Equity Incentive Plans Related to Stock Options

Activity under the Company’s equity incentive plans related to stock options is set forth below (in thousands except weighted average exercise price):

	Number of Options Outstanding			Weighted Average Exercise Price per Share
Balances at December 31, 2014		11,323		$	4.13
Granted		3,730			4.58
Forfeited		(225	)		5.12
Expired		(223	)		8.55
Exercised		(486	)		2.74
Balances at December 31, 2015		14,119			4.21

Information Regarding Stock Options Outstanding Stock Options Vested and Expected to Vest and Stock Options Exercisable

Information regarding the Company’s stock options outstanding, stock options vested and expected to vest, and stock options exercisable at December 31, 2015, was as follows (in thousands except weighted average exercise price and contractual term):

	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Balances at December 31, 2015
Stock options outstanding		14,119	$	4.21		6.9	$	30,746
Stock options vested and expected to vest		13,606		4.19		6.8		29,973
Stock options exercisable		8,693		3.81		5.7		22,754

Recognition of Stock-Based Compensation Expense

Stock-based compensation expense recognized on the Company’s consolidated statements of operations for the years ended December 31, 2015, 2014 and 2013, was as follows (in thousands):

	Year Ended December 31,
	2015		2014		2013
Stock-based compensation expense by caption:
Research and development	$	1,260	$	998	$	482
Selling, general and administrative		5,470		4,155		2,786
Total stock-based compensation expense	$	6,730	$	5,153	$	3,268

Weighted Average Assumptions Used to Value Stock-Based Awards

The weighted average assumptions used to value the Company’s stock-based awards for the years ended December 31, 2015, 2014 and 2013, was as follows:

	Year Ended December 31,
	2015			2014			2013
Stock Options:
Expected term (in years)		5.66			5.71			5.59
Estimated volatility		56	%		61	%		60	%
Risk-free interest rate		1.55	%		1.73	%		0.87	%
Expected dividend yield		0	%		0	%		0	%
Employee Stock Purchase Plan Rights:
Expected term (in years)		0.75			0.76			0.50
Estimated volatility		53	%		52	%		39	%
Risk-free interest rate		0.28	%		0.10	%		0.10	%
Expected dividend yield		0	%		0	%		0	%